Electrodeposited copper foils such as those disclosed in many literatures including Patent Document 1 and rolled copper foils such as the one disclosed in Patent Document 2 have been conventionally used for the manufacturing of copper-clad laminates. Then, the printed wiring boards have been manufactured by etching the copper layer constituting the copper-clad laminates.
The manufacturing methods of copper-clad laminates are different with their type, rigid type copper-clad laminates or flexible type copper-clad laminates. In manufacturing of the rigid type copper-clad laminates, the popular method is to sandwich a book in which copper foils, resin-impregnated base materials (prepregs) semi-cured to be B stage and mirror plates for spacers are stacked in multiple layers between hot plates, then the resin of the resin-impregnated base materials are cured under a high temperature and high pressure to bond them with the copper foils (hereinafter this process may be sometimes referred to as hot pressing). In manufacturing of the flexible type copper-clad laminates, the popular method is bonding a copper foil to an organic polymer material for the insulating layer, such as polyimide, by hot pressing or roll lamination, or forming a polyimide resin layer by coating a copper foil with a polyamic resin component by casting followed by heating.
On the other hand, printed wiring boards installed in latest downsized electronic equipment are required to have fine-pitch wirings with a view to increasing the packaging density of devices to arrange in the narrower space of the equipments. To qualify the requirement, the industry concerned has been tried to use thinner copper foils. However, the thinner copper foil is more difficult in handling to result defects such as wrinkling. When a copper foil has wrinkles, crack may be generated in wrinkle of copper foil in pressing process and the fluidized resin constituting the prepreg is made to ooze out and contaminate and/or worsen the flatness of the surface of the copper-clad laminate. Such defects of the copper-clad laminate surface may result short-circuit and/or open-circuit in the manufactured printed wiring board. Even when a method such as roll lamination or casting of not hot pressing is used in manufacturing flexible copper-clad laminates, wrinkles in the copper foils would remain as unevenness on the surface of the copper-clad laminates and it may cause similar kind of problems, short-circuit and/or open-circuit.
These problems have been driving force to use electrodeposited copper foils with carrier foil. Electrodeposited copper foil with carrier foil can be classified into the peelable type and the etchable type. Simply speaking, the difference is that the carrier foil on a copper-clad laminate of the peelable type is physically peeled off, but the carrier foil on the copper-clad laminate of the etchable type is etched off. In recent years, demands for peelable type electrodeposited copper foils with carrier foil which has advantage in manufacturing cost because etching process is not required have become significant. Patent Document 3, Patent Document 4 and others disclose peelable type electrodeposited copper foils with carrier foil.
The peelable type electrodeposited copper foil with carrier foil comprises a stacked structure composed of a release layer between a carrier foil layer and a copper foil layer. It is required to have a peelable characteristic for the carrier foil with release strength of 20 gf/cm to 100 gf/cm even after the thermal treatment in the hot pressing. The release strength tends to increase with the rise in hot pressing temperature. However, hot pressing with a liquid crystal polymer base material or a fluorine-containing resin base material are performed at a temperature of exceeding 300° C., and the formation of a polyimide resin layer by casting method adopts a temperature of exceeding 300° C. also. In such a case, when the release layer between the carrier foil layer and the copper foil layer has not enough thermal resistance, counter diffusion may occur between the carrier foil layer and the copper foil layer or among the three layers, carrier foil layer/release layer/copper foil layer, to result phenomenon that the carrier foil is partially torn off to remain on the surface of the copper foil layer or that the carrier foil layer cannot be released from the copper foil layer.
As a method relates to a copper foil with carrier foil which permits easy releasing of the carrier foil even after hot pressing at high temperature, Patent Document 3 discloses a method using just a metal oxide for a bonding interface layer between the carrier layer and the copper foil layer, which makes use the characteristic that the compound is stable at high temperature and generally hard but brittle.
Patent Document 4 discloses an ultra-thin copper foil with carrier formed by stacking a release layer, an anti-diffusion layer and an electrodeposited copper layer on a carrier foil in this order, and the surface of the electrodeposited copper layer is roughening treated. The release layer is an inorganic release layer, preferably a chromium layer or a chrome hydrated oxide layer. The anti-diffusion layer which prevents the diffusion of the release layer when the ultra-thin copper foil with carrier foil is laminated by hot pressing is formed on the release layer. The anti-diffusion layer may be composed of at least one selected from a group of elements comprising nickel, cobalt, iron, chromium, molybdenum, tungsten, copper, aluminum and phosphorus, and of a single metal or a layer of an alloy of two or more metals or of a metal oxide of one kind or more. This is intended to perform both the stability of release strength of the carrier foil after hot pressing and the laser drill ability.
Patent Document 5 discloses an ultra-thin copper foil with carrier foil stacking a carrier foil, a bonding interface layer formed of an organic agent and a copper foil layer in the order. As the bonding interface disclosed in Patent Document 5 is formed by an organic agent, stable or more stable release strength of the carrier foil can be performed than the electrodeposited copper foil with carrier foil disclosed in Patent Document 3 when hot pressed at or below 200° C. However, after hot pressing at a temperature exceeding 200° C., the carrier foil layer cannot be released from the copper foil layer.
By the way, when thiocyanuric acid is used for formation of the bonding interface layer as disclosed in Patent Document 6, it enables releasing of the carrier foil even when a hot pressing temperature is exceeding 300° C. As disclosed in Patent Document 7, as for an electrodeposited copper foil with carrier foil in which a bonding interface layer is formed on one surface of the carrier foil and a copper foil layer is formed on the bonding interface layer, and the bonding interface layer is formed of a metal oxide layer and an organic agent, carrier releasing is easy even after hot pressing at a temperature exceeding 200° C. The metal oxide layer constituting the bonding interface layer may be the oxide of nickel, chromium, titanium, magnesium, iron, cobalt or tungsten or an oxide of alloy containing these elements in a thickness by calculation of 1 nm or more.
As described above, methods for manufacturing a peelable type electrodeposited copper foil with carrier foil, which make releasing of the carrier foil easy even after a hot pressing at high temperature, have been proposed and are effective to some extent.    [Patent Document 1] Japanese Patent Application Laid-Open No. 10-18075    [Patent Document 2] Japanese Patent Application Laid-Open No. 8-158027    [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-502496 (EP 1133220)    [Patent Document 4] WO 2002/024444    [Patent Document 5] Japanese Patent Application Laid-Open No. 2000-309898    [Patent Document 6] Japanese Patent Application Laid-Open No. 2001-68804    [Patent Document 7] Japanese Patent Application Laid-Open No. 2003-181970